Some years ago TROPOS developed an inlet for the ground-based collection of small ice particles in mixed-phase clouds, the so-called Ice-CVI (Ice-CVI), which is unique until now. This inlet is especially adapted for the highest European research station Jungfraujoch (Forschungsstation Jungfraujoch), where the probability for the occurrence of mixed-phase clouds is maximal. There TROPOS takes part in the international CLACE (Cloud and Aerosol Characterization Experiment) cloud field measurement campaigns, actual CLACE2013 (CLACE2013), with the Ice-CVI. The scientific objectives concerning heterogeneous ice formation in real clouds and therefore concerning atmospheric ice nuclei (IN) are:
- Microphysical and chemical Characterization of residual particles from small ice crystals in atmospheric mixed-phase clouds
- Comparison of the microphysical and chemical properties of these ice particle residues (IPR) to atmospheric particles, which serve as IN inside ice nuclei countern
- Assignment of the atmospheric relevance of special aerosol types with respect to the heterogeneous ice formation in super-cooled clouds, inter alia for process studies in laboratory experiments
- Provision of input and validation parameters for cloud process simulations, which include heterogeneous ice nucleation
- Formulation of parameterizations of heterogeneous ice nucleation for large scale wheather and climate models
In order to attribute the analyzed IPR to atmospheric ice nuclei, the diameter of the sampled ice particles is restricted by the Ice-CVI to 20 µm, because the ice particles grow solely by water vapor diffusion until this size and collect hardly any interstitial aerosol. Larger ice crystals, interstitial aerosol particles and super-cooled drops are pre-segregated by means of several inlet components. The flows and geometries have dimensions, so that no ice particle shattering or drop break-up occur.
Besides the Ice-CVI a second CVI system was developed (IN-CVI), based on the pumped CVI principle, which separates ice particles activated in an ice nucleus counter. The ice phase becomes evaporated and the released IN are allocated for analysis. Both systems were operated during the field campaign CLACE 2013 within the DFG research unit INUIT (INUIT). Behind the two CVI systems, TROPOS measured number concentration and size distribution of IN and IPR.
The main results of previous CLACE campaigns and first findings from CLACE2013 are:
- The capability of aerosol particles to serve as heterogeneous ice nuclei starts at about 200 nm and the efficiency increases with increasing size (Mertes et. al (2007))
- In the examined ice particle residues soot was enriched in comparison to the background aerosol (Mertes et. al (2007); Cozic et al. (2008))
- The number concentration of the ice particle residues is several particles per liter, which is in the same order of magnitude as the observed small ice particles, whereas the number concentration of the ice nuclei obtained by a ice nucleus counter, is less by one or two orders of magnitude.
- The main components of the ice particle residues are mineral dust and carbonaceous particles, but biological particles could not be detected. Lead containing particles were found to be strongly enriched in the ice particle residues, which indicates their good ice nucleation capability (Cziczo et al (2009); Kamphus et. al (2010); Ebert et. al (2011))
- S. Mertes, B. Verheggen, S. Walter, P. Connolly, M. Ebert, J. Schneider, K. N. Bower, J. Cozic, S. Weinbruch, U. Baltensperger & E. Weingartner (2007), Counterflow virtual impactor based collection of small ice particles in mixed-phase clouds for the physico-chemical characterization of tropospheric ice nuclei: Sampler description and first case study, Aerosol Science and Technology 41(9): 848- 864, doi:10.1080/02786820701501881.
- J. Cozic, S. Mertes, B. Verheggen, D. J. Cziczo, S. J. Gallavardin, S. Walter, U. Baltensperger and E. Weingartner (2008), Black carbon enrichment in atmospheric ice particle residuals observed in lower tropospheric mixed phase clouds. Journal of Geophysical Research (D) 113(D15): D15209, doi:10.1029/2007JD009266.
- Daniel J. Cziczo, Olaf Stetzer, Annette Worringen, Martin Ebert, Stephan Weinbruch, Michael Kamphus, Stephane J. Gallavardin, Joachim Curtius, Stephan Borrmann, Karl D. Froyd, Stephan Mertes, Ottmar Möhler & Ulrike Lohmann (2009) Inadvertent climate modification due to anthropogenic lead, Nature Geoscience 2(5): 333-336.
- M. Kamphus, , M. Ettner-Mahl, T. Klimach, F. Drewnick, L. Keller, D. J. Cziczo, S. Mertes, S. Borrmann and J. Curtius (2010), Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: Single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6), Atmospheric Chemistry and Physics 10(16): 8077-8095.
- M. Ebert, A. Worringen, N. Benker, S. Mertes, E. Weingartner, and S. Weinbruch (2011), Chemical composition and mixing-state of ice residuals sampled within mixed phase clouds." Atmospheric Chemistry and Physics 11: 1-12.